NHC‐Catalyzed Michael Addition to α,β‐Unsaturated Aldehydes by Redox Activation

Through oxidative carbene catalysis the reactivity of enals can be reversed at the β position from the typical electrophilic to nucleophilic (homoenolate chemistry) further to electrophilic reactivity by two consecutive umpolung processes. These redox-activated Michael acceptors show higher reactivity at the β position than that for the starting enals. Their reactions with β-dicarbonyl compounds provide dihydropyranones in good to excellent yields under mild conditions.